A typical problem in phased array ultrasound (PAUT) NDT inspection utilizing multiple instruments is combining the data from multiple inspection instruments and obtaining phase-synchronous and frequency-synchronous data. Typically, the inspection instruments are neither synchronized in frequency nor in phase, making it hard to match the data from one instrument with another since they are not on the same time-base.
As the acquisition time gets longer, the problem is exacerbated. Assuming that one sub-instrument is the true time, the other sub-instruments acquire data slightly faster or slower. Thus, even if the data is synchronized using one particular NDT inspection feature, another inspection feature acquired at a later time is likely to be unsynchronized.
Inspection events with NDT instruments are often time critical. Having to adjust the phase and frequency of inspection features from multiple instruments can distract the effort of an inspection operator. Patent WO2010/017445A3 disclosed an apparatus that aims to increase the aperture of a medical ultrasound system using add-on ultrasound systems. However, clock synchronization is not performed. Instead, synchronization is performed by comparing the timing of received pulses from the different add-on instruments. This method is not good enough for industrial purposes because in industrial NDT data acquisition the acquisition time can be much longer, and time slip is more likely to occur. If one particular feature is time synchronized among multiple instruments, a feature acquired at a later time is likely to be unsynchronized because of the time slip.
A technical paper published on the Cornell University web site (“Multi-Channel Data Acquisition with Absolute Time Synchronization” by P. Wlodarczyk, S. Pustelny, D. Budker, and M. Lipiński) at http://arxiv.org/ftp/arxiv/papers/1311/1311.5849.pdf discloses a method to synchronize multiple channels of data on remote acquisition cards with absolute time synchronization. However, the application described in the paper is different from the one described in the present disclosure, and the sampling rate is about a thousand times slower. In contrast, the present invention deals with the most acute problems of consolidating data from multiple unsynchronized instruments.
Considering the background information above, a solution that provides a plurality of NDT instruments to service providers, while minimizing or eliminating manual adjustment of multiple phases and frequencies, would be of great utility and economic value.